/*
 * Copyright 2002-2012 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.util;

import org.springframework.util.Assert;

import java.io.ByteArrayOutputStream;
import java.io.UnsupportedEncodingException;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Utility class for URI encoding and decoding based on RFC 3986. Offers encoding methods for the various URI
 * components.
 *
 * <p>All {@code encode*(String, String} methods in this class operate in a similar way:
 * <ul>
 * <li>Valid characters for the specific URI component as defined in RFC 3986 stay the same.</li>
 * <li>All other characters are converted into one or more bytes in the given encoding scheme. Each of the
 * resulting bytes is written as a hexadecimal string in the "{@code %<i>xy</i>}" format.</li>
 * </ul>
 *
 * @author Arjen Poutsma
 * @see <a href="http://www.ietf.org/rfc/rfc3986.txt">RFC 3986</a>
 * @since 3.0
 */
public abstract class UriUtils {

    private static final String SCHEME_PATTERN = "([^:/?#]+):";

    private static final String HTTP_PATTERN = "(http|https):";

    private static final String USERINFO_PATTERN = "([^@/]*)";

    private static final String HOST_PATTERN = "([^/?#:]*)";

    private static final String PORT_PATTERN = "(\\d*)";

    private static final String PATH_PATTERN = "([^?#]*)";

    private static final String QUERY_PATTERN = "([^#]*)";

    private static final String LAST_PATTERN = "(.*)";

    // Regex patterns that matches URIs. See RFC 3986, appendix B
    private static final Pattern URI_PATTERN = Pattern.compile(
            "^(" + SCHEME_PATTERN + ")?" + "(//(" + USERINFO_PATTERN + "@)?" + HOST_PATTERN + "(:" + PORT_PATTERN +
                    ")?" + ")?" + PATH_PATTERN + "(\\?" + QUERY_PATTERN + ")?" + "(#" + LAST_PATTERN + ")?");

    private static final Pattern HTTP_URL_PATTERN = Pattern.compile(
            "^" + HTTP_PATTERN + "(//(" + USERINFO_PATTERN + "@)?" + HOST_PATTERN + "(:" + PORT_PATTERN + ")?" + ")?" +
                    PATH_PATTERN + "(\\?" + LAST_PATTERN + ")?");

    // encoding

    /**
     * Encodes the given source URI into an encoded String. All various URI components are
     * encoded according to their respective valid character sets.
     * <p><strong>Note</strong> that this method does not attempt to encode "=" and "&"
     * characters in query parameter names and query parameter values because they cannot
     * be parsed in a reliable way. Instead use:
     * <pre>
     * UriComponents uriComponents = UriComponentsBuilder.fromUri("/path?name={value}").buildAndExpand("a=b");
     * String encodedUri = uriComponents.encode().toUriString();
     * </pre>
     *
     * @param uri      the URI to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded URI
     * @throws IllegalArgumentException     when the given uri parameter is not a valid URI
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     * @deprecated in favor of {@link UriComponentsBuilder}; see note about query param encoding
     */
    @Deprecated
    public static String encodeUri(String uri, String encoding) throws UnsupportedEncodingException {
        Assert.notNull(uri, "'uri' must not be null");
        Assert.hasLength(encoding, "'encoding' must not be empty");
        Matcher m = URI_PATTERN.matcher(uri);
        if (m.matches()) {
            String scheme = m.group(2);
            String authority = m.group(3);
            String userinfo = m.group(5);
            String host = m.group(6);
            String port = m.group(8);
            String path = m.group(9);
            String query = m.group(11);
            String fragment = m.group(13);

            return encodeUriComponents(scheme, authority, userinfo, host, port, path, query, fragment, encoding);
        } else {
            throw new IllegalArgumentException("[" + uri + "] is not a valid URI");
        }
    }

    /**
     * Encodes the given HTTP URI into an encoded String. All various URI components are
     * encoded according to their respective valid character sets.
     * <p><strong>Note</strong> that this method does not support fragments ({@code #}),
     * as these are not supposed to be sent to the server, but retained by the client.
     * <p><strong>Note</strong> that this method does not attempt to encode "=" and "&"
     * characters in query parameter names and query parameter values because they cannot
     * be parsed in a reliable way. Instead use:
     * <pre>
     * UriComponents uriComponents = UriComponentsBuilder.fromHttpUrl("/path?name={value}").buildAndExpand("a=b");
     * String encodedUri = uriComponents.encode().toUriString();
     * </pre>
     *
     * @param httpUrl  the HTTP URL to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded URL
     * @throws IllegalArgumentException     when the given uri parameter is not a valid URI
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     * @deprecated in favor of {@link UriComponentsBuilder}; see note about query param encoding
     */
    @Deprecated
    public static String encodeHttpUrl(String httpUrl, String encoding) throws UnsupportedEncodingException {
        Assert.notNull(httpUrl, "'httpUrl' must not be null");
        Assert.hasLength(encoding, "'encoding' must not be empty");
        Matcher m = HTTP_URL_PATTERN.matcher(httpUrl);
        if (m.matches()) {
            String scheme = m.group(1);
            String authority = m.group(2);
            String userinfo = m.group(4);
            String host = m.group(5);
            String portString = m.group(7);
            String path = m.group(8);
            String query = m.group(10);

            return encodeUriComponents(scheme, authority, userinfo, host, portString, path, query, null, encoding);
        } else {
            throw new IllegalArgumentException("[" + httpUrl + "] is not a valid HTTP URL");
        }
    }

    /**
     * Encodes the given source URI components into an encoded String. All various URI components
     * are optional, but encoded according to their respective valid character sets.
     *
     * @param scheme    the scheme
     * @param authority the authority
     * @param userInfo  the user info
     * @param host      the host
     * @param port      the port
     * @param path      the path
     * @param query     the query
     * @param fragment  the fragment
     * @param encoding  the character encoding to encode to
     * @return the encoded URI
     * @throws IllegalArgumentException     when the given uri parameter is not a valid URI
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     * @deprecated in favor of {@link UriComponentsBuilder}
     */
    @Deprecated
    public static String encodeUriComponents(String scheme, String authority, String userInfo,
                                             String host, String port, String path, String query, String fragment, String encoding)
            throws UnsupportedEncodingException {

        Assert.hasLength(encoding, "'encoding' must not be empty");
        StringBuilder sb = new StringBuilder();

        if (scheme != null) {
            sb.append(encodeScheme(scheme, encoding));
            sb.append(':');
        }

        if (authority != null) {
            sb.append("//");
            if (userInfo != null) {
                sb.append(encodeUserInfo(userInfo, encoding));
                sb.append('@');
            }
            if (host != null) {
                sb.append(encodeHost(host, encoding));
            }
            if (port != null) {
                sb.append(':');
                sb.append(encodePort(port, encoding));
            }
        }

        sb.append(encodePath(path, encoding));

        if (query != null) {
            sb.append('?');
            sb.append(encodeQuery(query, encoding));
        }

        if (fragment != null) {
            sb.append('#');
            sb.append(encodeFragment(fragment, encoding));
        }

        return sb.toString();
    }


    // encoding convenience methods

    /**
     * Encodes the given URI scheme with the given encoding.
     *
     * @param scheme   the scheme to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded scheme
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodeScheme(String scheme, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents.encodeUriComponent(scheme, encoding,
                HierarchicalUriComponents.Type.SCHEME);
    }

    /**
     * Encodes the given URI authority with the given encoding.
     *
     * @param authority the authority to be encoded
     * @param encoding  the character encoding to encode to
     * @return the encoded authority
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodeAuthority(String authority, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents.encodeUriComponent(authority, encoding,
                HierarchicalUriComponents.Type.AUTHORITY);
    }

    /**
     * Encodes the given URI user info with the given encoding.
     *
     * @param userInfo the user info to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded user info
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodeUserInfo(String userInfo, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents.encodeUriComponent(userInfo, encoding,
                HierarchicalUriComponents.Type.USER_INFO);
    }

    /**
     * Encodes the given URI host with the given encoding.
     *
     * @param host     the host to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded host
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodeHost(String host, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents
                .encodeUriComponent(host, encoding, HierarchicalUriComponents.Type.HOST);
    }

    /**
     * Encodes the given URI port with the given encoding.
     *
     * @param port     the port to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded port
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodePort(String port, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents
                .encodeUriComponent(port, encoding, HierarchicalUriComponents.Type.PORT);
    }

    /**
     * Encodes the given URI path with the given encoding.
     *
     * @param path     the path to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded path
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodePath(String path, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents
                .encodeUriComponent(path, encoding, HierarchicalUriComponents.Type.PATH);
    }

    /**
     * Encodes the given URI path segment with the given encoding.
     *
     * @param segment  the segment to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded segment
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodePathSegment(String segment, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents.encodeUriComponent(segment, encoding,
                HierarchicalUriComponents.Type.PATH_SEGMENT);
    }

    /**
     * Encodes the given URI query with the given encoding.
     *
     * @param query    the query to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded query
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodeQuery(String query, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents
                .encodeUriComponent(query, encoding, HierarchicalUriComponents.Type.QUERY);
    }

    /**
     * Encodes the given URI query parameter with the given encoding.
     *
     * @param queryParam the query parameter to be encoded
     * @param encoding   the character encoding to encode to
     * @return the encoded query parameter
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodeQueryParam(String queryParam, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents.encodeUriComponent(queryParam, encoding,
                HierarchicalUriComponents.Type.QUERY_PARAM);
    }

    /**
     * Encodes the given URI fragment with the given encoding.
     *
     * @param fragment the fragment to be encoded
     * @param encoding the character encoding to encode to
     * @return the encoded fragment
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     */
    public static String encodeFragment(String fragment, String encoding) throws UnsupportedEncodingException {
        return HierarchicalUriComponents.encodeUriComponent(fragment, encoding,
                HierarchicalUriComponents.Type.FRAGMENT);
    }


    // decoding

    /**
     * Decodes the given encoded source String into an URI. Based on the following rules:
     * <ul>
     * <li>Alphanumeric characters {@code "a"} through {@code "z"}, {@code "A"} through {@code "Z"}, and
     * {@code "0"} through {@code "9"} stay the same.</li>
     * <li>Special characters {@code "-"}, {@code "_"}, {@code "."}, and {@code "*"} stay the same.</li>
     * <li>A sequence "{@code %<i>xy</i>}" is interpreted as a hexadecimal representation of the character.</li>
     * </ul>
     *
     * @param source   the source string
     * @param encoding the encoding
     * @return the decoded URI
     * @throws IllegalArgumentException     when the given source contains invalid encoded sequences
     * @throws UnsupportedEncodingException when the given encoding parameter is not supported
     * @see java.net.URLDecoder#decode(String, String)
     */
    public static String decode(String source, String encoding) throws UnsupportedEncodingException {
        Assert.notNull(source, "'source' must not be null");
        Assert.hasLength(encoding, "'encoding' must not be empty");
        int length = source.length();
        ByteArrayOutputStream bos = new ByteArrayOutputStream(length);
        boolean changed = false;
        for (int i = 0; i < length; i++) {
            int ch = source.charAt(i);
            if (ch == '%') {
                if ((i + 2) < length) {
                    char hex1 = source.charAt(i + 1);
                    char hex2 = source.charAt(i + 2);
                    int u = Character.digit(hex1, 16);
                    int l = Character.digit(hex2, 16);
                    if (u == -1 || l == -1) {
                        throw new IllegalArgumentException("Invalid encoded sequence \"" + source.substring(i) + "\"");
                    }
                    bos.write((char) ((u << 4) + l));
                    i += 2;
                    changed = true;
                } else {
                    throw new IllegalArgumentException("Invalid encoded sequence \"" + source.substring(i) + "\"");
                }
            } else {
                bos.write(ch);
            }
        }
        return changed ? new String(bos.toByteArray(), encoding) : source;
    }

}
